Not applicable.
Not applicable.
Heart rate variability has been measured and evaluated to provide an indicator of a patient""s autonomic nervous system function. The autonomic nervous system, including the sympathetic and parasympathetic systems, governs involuntary actions of cardiac muscle and certain body tissue. Autonomic neuropathy affects the nerves that serve the heart and internal organs and produces changes in many processes and systems. Autonomic neuropathy is most commonly linked to diabetes; however, several causes are possible, including alcoholism, sleep apnea, and coronary artery disease. Thus, evaluation of the autonomic nervous system function has wide applicability, from diagnosing and treating patients with diabetes to detecting patients at risk for sudden death due to cardiac arrest.
Heart rate variability monitors perform signal analysis on physiological signals, such as ECG signals, in order to measure the interval between certain phenomena, such as the interval between peaks (i.e., R-waves) of the QRS complex, or the Rxe2x80x94R interval, to provide an indication of heart rate versus time. Methods and apparatus for accurately detecting Rxe2x80x94R intervals are described in U.S. Pat. No. 5,984,954, entitled xe2x80x9cMethods and Apparatus for R-Wave Detection.xe2x80x9d
Various tests have been developed to exercise the autonomic nervous system for purposes of measuring heart rate variability. Two illustrative tests are the Valsalva test and the Expiration/Inspiration (E/I) test, which is sometimes referred to as the metronomic test. The Valsalva test requires that the patient forcibly exhale to a predetermined pressure, such as 40 mmHg, for a predetermined duration, such as 15 seconds, during which the heart rate is monitored. Thereafter, the patient rests for a predetermined duration. The result of the Valsalva test is a ratio of the highest heart rate (as indicated by the shortest R-R interval) during the breathing maneuver to the lowest heart rate (as indicated by the longest Rxe2x80x94R interval) during a recovery period after the lo maneuver. In accordance with the E/I test, the patient is instructed to breathe deeply at a frequency of 6 cycles/minute, which has been shown to produce maximal heart rate variability in healthy individuals. The result of the E/I test is a ratio of the average of the heart rate peaks to the average of the heart rate troughs. Several other tests for exercising the autonomic nervous system are used, including the standing test in which the patient""s heart rate in both supine and standing positions are compared, and frequency under the power spectrum density curve tests.
Heart rate variability tests are generally performed in a physician""s office, at a hospital, or other medical facility. The accuracy of the test results is a function of many factors including the extent to which a patient complies with the particular breathing regimen of the test, the signal processing techniques used to evaluate heart rate variability, and the skill of the medical technician or other operator of the heart rate monitor in administering the test.
It is an object of the present invention to improve the accuracy of heart rate variability test results.
It is a further object of the invention to facilitate training of medical personnel operating heart rate monitors in order to further improve the accuracy of heart rate variability test results.
These and other objects of the invention are achieved by a heart rate variability system including heart rate monitors for collecting physiological data from patients at a medical facility and a processing center located remotely from, and in communication with the heart rate monitors. The processing center receives the physiological data and analyzes the data to provide test results based on the patient""s heart rate variability and indicative of the patient""s autonomic nervous system function. The processing center may transmit the results to the heart rate monitor at which the data was collected. In one illustrative embodiment, the analysis performed at the processing center includes use of an automated technique for detecting Rxe2x80x94R intervals and also includes intervention by a trained analyst to more accurately identify Rxe2x80x94R intervals and anomalies in the resulting heart rate versus time waveform. With this arrangement, the accuracy of the heart rate variability test results is improved due to the use of rigorous automated heart rate variability detection techniques at the processing center and intervention by trained analysts.
Also described is a medical testing system including collection devices for collecting physiological data from patients at a medical facility and a remote processing center for analyzing the physiological data, with each of the collection devices including a display for displaying a waveform showing the patient""s performance during collection of the data. Also displayed are performance standards against which to compare the performance waveform in order to determine the extent to which the patient followed a predetermined breathing maneuver during data collection. A user interface of the heart rate monitors is responsive to inputs indicating acceptance of the physiological data if the comparison reveals less than a predetermined deviation between the performance waveform and the performance standards or rejection of the physiological data if the comparison reveals greater than a predetermined deviation. In one embodiment, the test results are compared to predetermined acceptance criteria at the processing center and are rejected if the comparison reveals greater than a predetermined deviation between the results and the predetermined acceptance criteria.
With this arrangement, the accuracy of the test results provided by the processing center is enhanced, since such test results are based only on raw physiological data collected during xe2x80x9cwell-performedxe2x80x9d testing. Stated differently, errors in test results caused by poor test taking are reduced. Thus, because bad physiological data generally will be rejected by the operator of the heart rate monitors and test results falling outside of predetermined acceptance criteria are rejected at the processing center, the accuracy and reproducibility of the tests is improved.
According to a further aspect of the invention, a medical testing system utilizes at least two, redundant processing centers. The system includes at least one collection device in communication with first and second processing centers, each operable to receive physiological data from the collection device, analyze the physiological data to provide a test result, and optionally transmit the test result back to the collection device. In one embodiment, the collection device randomly selects one of the processing centers for receipt of physiological data.
The use of two processing centers advantageously provides analyst availability even in the event of a failure at one of the processing centers or in the communication link to one of the processing centers. Further, use of two processing centers in the medical testing environment of the present invention provides the additional advantage of permitting system changes to be made and extensive, Federally mandated testing to be performed without impacting processing center access, since testing can be performed at one processing center while the other processing center supports collection devices.
The two processing centers are interconnected, preferably by two, redundant communication links. In normal operation, physiological data transmitted to either processing center and test results generated at either processing center are replicated for storage at the other processing center. With this arrangement, since all patient test results are stored at both processing centers, either processing center is capable of providing historical, or trending data to patients and their physicians. Further, in the case of a fault at one of the processing centers relating to its ability to analyze data and generate test results, the unanalyzed physiological data can be analyzed at the other processing center.